Astronomical watches are among the watches with complications appreciated by users. Their accuracy is often approximate as regards the display of the cycles of certain celestial bodies, in particular lunar cycles, often because of the small volume available inside the movement, which generally cannot house the large number of wheels which would be necessary to ensure an accurate estimate of the duration of the lunar day and month.
Further, it is often impractical to view the celestial body phases. Most timepiece displays have abandoned the illustration of the celestial body day.
WO Patent No 91/11756 A1 in the name of Richard discloses a Moon display with a first circular plate whose rotation is maintained by a drive mechanism of the watch, with a sphere representing the Moon, able to be moved with this circular support along an aperture arranged in the watch dial. The drive mechanism includes a means of driving the circular support in rotation relative to the aperture, at a speed in keeping with the speed of the apparent movement of the Moon in the sky between rising and setting. The mechanism drives in rotation a second plate at a similar speed to that of the first plate, the second plate drives a pinion which causes the sphere to turn about an axis parallel to the watch dial.
The technical article of the Jahrbuch der deutschen Gesellschaft für Chronometrie, in the name of GLASER <<Astronomische Indikationen bei Uhren>>, published on 1 Jan. 1989, vol. 40, pages 139-161, XP000102620, ISSN 0373-7616, discloses a representation of the Moon phases by means of a rotating sphere or rotating discs. A differential drive element drives at suitable speeds both the sphere in rotation on its arbour, and the arbour relative to the dial.
U.S. Pat. No. 3,766,727A in the name of DIDIK discloses a planet clock with a complex gear train driving the planets of the solar system represented by spheres, with the Moon pivoting about the Earth mounted on an inclined arbour, and wherein the driving of the inclined Earth arbour, the Earth about the arbour, and the Moon about the Earth, is performed by as many pulleys in mesh with axial cannon-pinions of the movement.
FR Patent No 12 679 052 A1 in the name of GHIRIMOLDI discloses a planetarium timepiece mechanism with a solid representation.
FR Patent No 348 040 A in the name of Burke discloses an astronomical clock with some celestial bodies motorised with respect to others.